Position-measuring transformer having end-detecting windings useful for positioning a magnetic head of a disc drive system

ABSTRACT

Disclosed is a position-measuring transformer formed from two relatively movable members. The transformer is particularly useful for selecting and defining track positions in a magnetic disc drive system which may be used as a memory in a digital computer. One stationary member of the transformer includes cofunction windings and end-detecting windings. Those windings magnetically coupled to a reference winding on another relatively movable member of the transformer. The reference winding, which is the continuous winding of the transformer, is formed from a plurality of equally spaced active conductors. The active conductors are interconnected such that alternate ones conduct in opposite directions so that each pair of adjacent active conductors define a reference cycle. The end-detecting windings consist of one or more pairs of active conductors where the active conductors in each pair have full-cycle spacing, that is, the separation between each active conductor in a pair equals one reference cycle. The full-cycle spacing of the end-detecting winding superposed over the half-cycle spacing of the enddetecting winding induces a substantially zero resultant signal in the end-detecting winding except when the end-detecting winding is positioned over the end conductor of the reference winding as may occur when the reference winding is moved. When over the end, a limit signal is generated as a result of the unequal coupling between the end-detecting winding active conductors and the end conductor of the reference winding. The limit signal thus generated typically defines the inner or outer limit of a read/write head. Cofunction windings are formed from four winding sections with equal numbers of active conductors per section. The cofunction windings are formed using an efficient winding pattern which minimizes the number of welded or soldered connections required.

United States Patent Farrand 1451 June 27, 1972 [54] POSITION-MEASURINGTRANSFORMER HAVING END- DETECTING WINDINGS USEFUL FOR POSITIONING AMAGNETIC HEAD OF A DISC DRIVE SYSTEM Clair L. Far-rand, Bronxville, NY.

731 Assignee: lnductosyn Corporation, Valhalla, NY. 22 Filed: March a,1971 [211 App]. No.: 121,951

[72] Inventor:

Primary Examiner-Bemard Konick Assistant Examiner-Vincent P; CanneyAttorney-William E. Beatty and David E. Lovejoy [57] ABSTRACT Disclosedis a position-measuring transfonner formed from two relatively movablemembers. The transformer is particularly useful for selecting anddefining track positions in a magnetic disc drive system which may beused as a memory in a digital computer. One stationary member of thetransformer includes cofunction windings and end-detecting windings.Those windings magnetically coupled to a reference winding on anotherrelatively movable member of the transformer. The reference winding,which is the continuous winding of the transformer, is formed from aplurality of equally spaced active conductors. The active conductors areinterconnected such that alternate ones conduct in opposite directionsso that each pair of adjacent active conductors define a referencecycle. The end-detecting windings consist of one or more pairs of activeconductors where the active conductors in each pair have full-cyclespacing, that is, the separation between each active conductor in a pairequals one reference cycle. The fullcycle spacing of the end-detectingwinding superposed over the half-cycle spacing of the end-detectingwinding induces a substantially zero resultant signal in theend-detecting winding except when the end-detecting winding ispositioned over the end conductor of the reference winding as may occurwhen the reference'winding is moved. When over the end, a limit signalis generated as a result of the unequal coupling between theend-detecting winding active conductors and the end conductor of thereference winding. The limit signal thus generated typically defines theinner or outer limit of a read/write head. Cofunction windings areformed from four winding sections with equal numbers of activeconductors per section. The cofunction windings are formed using anefficient winding pattern which minimizes the number of welded orsoldered connections required.

12 Clalns, 7 Drawing Figures POSITION-MEASURING TRANSFORMER HAVING END-DETECTING WINDINGS USEFUL FOR POSITIONING A MAGNETIC HEAD OF A DISCDRIVE SYSTEM BACKGROUND OF THE INVENTION This invention relates toposition-measuring transformers of the type having two relativelymovable members, one member having at least two planar windings (calledpolyphase windings) which are phase shifted in space relative to eachother and which are inductively coupled to another planar windingcarried by the other member.

When one winding on one member is energized with an altemati ng primarysignal, that winding induces a secondary signal in any winding ontheother member which is in close proximity thereto.

Conventional position-measuring transformers employ, on one member, asingle winding formed from uniformly spaced, series-connected activeconductors. That member is therefore a single-phasemember which definesa reference pitch, that is, defines a periodic spacing of the activeconductors. Two active conductors (two pitches) form a reference cycle.In practice, the single-phase member is called the scale for lineardevices and is called rotor" for rotary devices.

The other relatively movable member, called the polyphase member, ofconventional position-measuring transformers generally includes twocofunction windings, each phaseshifted in space with respect to theother a fractional portion of the reference cycle so that two differentphases are presented as determined with reference to the single-phasemember. In practice, the polyphase member is called the slider" forlinear devices and the stator for rotary devices. Notwithstandingconventional practice, either or both the single-phase or polyphasemembers can be movable.

The phase-shift between th e polyphase windings is generally one-quarterof the reference winding cycle. Accordingly, the phase shift between thepolyphase windings is a quadrature phase shift and hence is a phaseshift analogous to the quadrature phase shift between sine and cosinetrigonometric functions. When the polyphase windings are spaced in oddmultiples of a quarter cycle, they are conventionally identified as thesine and cosine windings. While sine and cosine windings areconventional, other phase shifts, of course, may be implemented. Forexample, 120 shifts between each of three windings may be employed toform a three-phase system. Broadly, the term polyphase" describes allsuch phaseshifted windings. Additionally, the term cofunction is alsogenerically used to describe the polyphase relations of windings ofposition-measuring transformers since sine and cosine, for example, aretrigonometric cofunctions of the same angle.

Position-measuring transformers of the above type have been known andused for many years. For example, US. Pat. Nos. 2,799,835; 2,915,722;2,924,798 and 3,441,888, all assigned to the assignee of the presentinvention, are representative examples. The V. F. Foster application,Multilayer Polyphasev Winding Member and Transformer," Ser. No. 36,913,filed May 13, 1970, assigned to the same assignee, discloses placingwinding sections of cofunction windings on different layers to solve thecrossover problem resulting from interconnecting winding sections. Whiletwo or more layers are useful, it is still desirable to reduce thenumber of crossovers required.

The development of data processing systems and particularly magneticdisc systems has produced a demand for greater information storagedensities. Such greater densities are achieved in disc systems bystoring data in more closely spaced magnetic tracks. Whileposition-measuring transformers have been widely employed for accuratelymeasuring and controlling machine elements at closely spaced positions,the magnetic disc drive systems have special requirements not heretoforereadily available from position-measuring transformers. One suchrequirement is the ability to detect inner and outer track limits beyondwhich the read/write head normally does not travel while also preciselydetecting crowded internal track positions between the inner and outerlimits.

It is an objective of the present invention, therefore, to provide aposition-measuring transformer which more efficiently and moreeconomically provides inner and outer limit indications while alsoprecisely indicating internal track locations.

SUMMARY OF THE INVENTION The present invention is an improved windingmember and position-measuring transformer which minimizes the number ofsoldered or welded wire connections and which defines space positionsuseful, for example, in controlling the read/write-head position inmagnetic disc drive systems.

The position-measuring transformer of the present invention includesend-detecting windings which are unresponsive to a reference windingexcept at special space positions. Additionally, cofunction windings areformed from four winding sections in a configuration which minimizes thenumber of soldered or welded winding connections required.

The sine and cosine windings and the end-detecting windings of thetransformer are positioned on one of two relatively movable members. Theother of the two relatively movable members supports a reference windingwhich establishes the periodic space cycle. The two members arepositioned in close proximity so that the windings magnetically couple.The reference winding is formed from a plurality of equally spacedactive conductors. The active conductors are positioned at half-cyclepoints and are interconnected by inactive conductors so that adjacentactive conductors carry current in opposite directions. Theend-detecting windings are formed from at least two active conductorswhich are spaced at full-cycle points, that is, at twice the spacing asthat between the reference winding active conductors.

The active conductors of the end-detecting windings are interconnectedby inactive conductors so that adjacent conductors conduct current inopposite directions. Whenever all the active conductors of theend-detecting windings are fully positioned over the active conductorsof the reference windings, the total resultant magnetic coupling in theend-detecting winding is substantially zero. Whenever the relativelymovable members are moved such that one or more of the active conductorsof an end-detecting winding does not fully couple the reference winding,for example when positioned over the end conductors, non-cancellingunequal coupling results in the generation of a limit signal.

In a magnetic disc drive embodiment, the end-detecting windings becomelocated over the ends of the reference winding when, for example, thereference winding member is translated. Whenever translation causes adetecting winding to exhibit a signal, that signal, as detected by asignal detector, signifies that an inner or outer limit has beenreached.

For locating intermediate tracks between the inner and outer tracklimits, cofunction sine and cosine windings produce signals at thecyclic positions established by the spacing of the reference conductors.The efiicient cofunction winding pattern which minimizes the number ofwelded or soldered connections is formed with four winding sections percofunction winding, that is, four for the sine winding and four for thecosine winding. The number of active conductors per winding section is afunction of the total number of active conductors in the polyphasewinding. For example, for a polyphase winding with 48 active conductors,each winding section includes six active conductors. For a lineartransformer, the sine and cosine winding sections are alternated with areversal of alternation at the center in order to employ the inventionof the above-referenced US. Pat. No. 2,915,722. As a specific example, apolyphase winding member which has 48 active conductors typicallyincludes in order six active conductors interconnected to form a sinewinding section, six active conductors interconnected to form a cosinewinding section, six active conductors forming a sine winding section,twelve active conductors forming two sideby-side cosine windingsections, six active conductors forming a sine winding section, sixactive conductors forming a cosine winding section and six activeconductors forming a sine winding section.

The spacing of the active conductors in the polyphase winding membernominally equals the spacing of the active conductors in the referencewinding member. The sine winding sections are, however, shifted withrespect to the cosine winding sections by a quarter cycle (or any oddintegral multiple thereof) of the reference winding cycle.

The end-detecting windings are typically positioned at either end of thesine and cosine windings. The end-detecting windings together with thecofunction windings operate with electronic signal detectors to defineand control the positions of tracks on a magnetic disc.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged schematic planview of a polyphase member, including end-detecting windings andcofunction windings and a single-phase member, including a referencewinding, where the two members, when superposed as in FIG. 3, form aposition-measuring transformer.

FIGS. 2a, 2b, 2c and 2d schematically depict several representativepositions of an end-detecting winding superposed over a referencewinding.

FIG. 3 depicts a schematic oblique view of a position-measuringtransformer of the FIG. I type mounted and connected in a magnetic discdrive system.

FIG. 4 depicts a cross-sectional front view of a portion of theposition-measuring transformer represented in FIG. 1.

DETAILED DESCRIPTION General FIG. 1 depicts a position-measuringtransformer including a olyphase member 49 which is stationary withrespect to a translatable single phase member 50. Polyphase member 49includes first and second end-detecting windings 30 and 31,respectively, and polyphase windings 48.

The member 50 includes the continuous reference winding 51 having aplurality of active conductors postscripted 43 and 44 which are spacedat half-cycle intervals, P, that is, with a pitch, P. The activeconductors postscripted 43 are connected to the active conductorspostscripted 44 by inactive conductors postscripted 45. Activeconductors 43 are operative to conduct current in one direction whilethe active conductors 44 are operative to conduct the same current inthe opposite direction. The distance between two alternate successiveactive conductors such as between typical conductors 43-1 and 43-2 or44-1 and 4 L-2, defines one full cycle, 2?, of reference winding 51.

End-Detecting Windings The end-detecting windings 30 and 31 each includeactive conductors 30-28 and 30-27 and 31-28 and 31-27, respectively. Thespacing between the active conductors 30-28 and 30-27 is one full cycle,2?, as is the spacing between the active conductors 31-28 and 31-27.Each of the active conductors of end-detecting windings 30 and 31 areconnected by an inactive conductor 30-32 and 31-32, respectively.Accordingly, any current conducted by active conductors 30-28 is in theopposite direction of an equal current carried by active conductor30-27. Similarly, any current in active conductor 31-28 is equal andopposite to the current in active conductor 31-27. If the magneticcoupling from reference winding 51 is equal for both active conductors30-28 and 30-27, then the resultant coupling in the end-detectingwinding 30 is substantially zero.

Similarly, for equal magnetic couplings in active conductors 31-28 and31-27, the resultant current in end-detecting winding 31 is alsosubstantially 0.

Referring to FIGS. 20 through 2d, an enlarged view of a referencewinding 51' and a superposed end-detecting winding 30 is shown. Theprimed numbers in FIGS. 2a through 2d correspond to the unprimed numbersof FIG. 1.

In FIG. 2a, it is assumed that terminals 40' and 41' are connected in aconventional manner to an AC signal generator and, therefore, an ACsignal is carried by reference winding 51'. With such a signal, activeconductor 43'-! induces a signal in active conductor 31-28'. In ananalogous manner, active conductor 44'-l induces an equal but oppositesignal in active conductor 31-28' so that the resultant signal in activeconductor 31-28' is substantially zero. In a similar manner, theresultant signal in active conductor 31-27' is also substantially zeroso that the signal between terminals 37' and 38 is also substantiallyzero.

Referring to FIG. 2b, end-detecting winding 31' is shifted to the rightrelative to its position in FIG. 2a so that active conductor 31-28 is nolonger equally spaced between active conductors 43-1 and 44-l. Theresultant signal in activeconductor 31-28, therefore, has a greatercontribution from active conductor 44'-l than from active conductor43'-1 since it is closer to active conductor 44'-1. In a similar manner,active conductor 31-27' has a greater component of coupling from activeconductor 44'-2 than from active conductor 43'-2. Since the signals ineach pair of like-numbered active conductors 44'-] and 44'-2, and 43'-land 43'-2 are equal and of the same direction, they induce equal signalcomponents into active conductors 31-28' and 31-27'. Since, however,active conductors 311-28 and 31-27' are interconnected by inactiveconductor 31-32' so as to conduct in opposite directions, the equalsignal in active conductors 31-28' and 31-27' are cancelled. Theresultant signal in end-detecting winding 31', of FIG. 2b as measuredbetween terminals 37 and 38', is substantially zero.

In FIG. 2c, again the equal resultant signals in active conductors31-28' and 31-27 are interconnected by inactive conductor 31-32' inopposite directions so that again the resultant signal is substantiallyzero.

Referring to FIG. 2d, the resultant signal between terminals 35' and 36'of end-detecting winding 30', unlike FIGS. 2a, 2b and 2c issubstantially greater than zero. This non-zero signal results becausethe end-detecting winding 31 partially extends over the end of thereference winding 51'. Because of this extension over the end, unequalcoupling occurs in active conductors 31-28 and 31-27'. The greatestcontribution to coupling in active conductor 31-28 is from activeconductor 43-2. There is no active conductor on the right-hand side ofactive conductor 31-28. Accordingly, a greater signal is induced inactive conductor 31-28' than is induced in active conductor 31-27'. Thisgreater signal, as increased by the active conductor 31-28' signal,results in a substantially greaterthan-zero signal between terminals 35'and 36'.

Summarizing FIGS. 2a through 2d, whenever the end-detecting winding 31'is fully positioned over the reference winding 51', in any positionrelative to the reference winding cycle, the resultant signal in winding31 is substantially zero. Whenever the end-detecting winding 31 is overthe end of the reference winding 51' through translation of member 50,unequal coupling occurs and a non-zero resultant signal is produced.Because the end-detecting windings have substantially zero signalwhenever fully positioned over the reference winding, they areunresponsive to the reference winding. Cofunction Windings Referringagain to FIG. 1, the polyphase windings 48 on member 49, like theend-detecting windings 30 and 31, magnetically couple the referencewinding 51 on member 50. A sine winding is formed between terminals 60and 61 by interconnected active conductors having postscripts 27 or 28.Similarly, a cosine winding is formed between terminals 63 and 64 againby interconnected active conductors having postscripts 27 or 28. Theactive conductors of the sine winding are formed into four windingsections SI, SII, SIII and SIV. Similarly, the active conductors of thecosine winding are formed into four winding sections CI, CII, CH1 andCIV. Winding section SI includes six active conductors I-28, 1-27, 2-28,2-27, 3-28 and 3-27. In a similar manner, winding sections SII, SIII andSW have six active conductors designated by the appropriate postscripts.In an analogous manner, cosine winding section CI includes activeconductors 4-28, 4-27, and so on, to 6-27. Cosine winding sections CII,CIII and CIV similarly have six active conductors designated by theapropriate postscripts.

In FIG. 1, the spacing between active conductors in each of eightwinding sections is nominally equal to the spacing, P, of the referencewinding 51. While the compression of active conductors for the purposeof harmonic suppression, as described in the R. W. Tripp US. Pat. No.2,799,835 is preferred, that compression has not been represented in theschematic representation of FIG. 1. While the spacing between activeconductors in a winding section is nominally P, the sine windingsections SI, SII, S111 and SIV are shifted relative to the cosinewinding sections CI, CII, CHI and CIV a quarter of the reference windingcycle, 2P, that is, /4)(2P)= (9%)). For example, the spacing betweenwinding sections SI and CI as measured between the active conductors3-27 and 4-28 is (3/2 )P which is equal to of a cycle, 2?. A similar5'4- cycle spacing appears between winding sections CI and SII, SII andCII, CIII and SIII, Slll and CIV, and CIV and SIV.

The sine winding sections SI through SIV are interconnected in oppositeconduction directions. Specifically, terminal 77 for winding section 51is connected to terminal 79 of section SII so that for a current in onedirection in active conductor 1-28 is matched by an equal but oppositedirection current in active conductor 7-28. The position of activeconductor 7-28 is midway between active conductors 43-5 and 44-5 ofreference winding 51. For the same relative displacement of members 49and 50, active conductor 1-28 is spaced midway between active conductors43-3 and 44-3 of reference winding 51. Accordingly, while conductors1-28 and 7-28 are interconnected so that current is in oppositedirections, they are also positioned with respect to the referencewinding so that they magnetically couple in the opposite sense. Theeffect resulting from opposite current directions cancels the effectresulting from opposite magnetic coupling in a manner which surpassesunwanted error-causing signals which would result from l-turn loopcoupling. Sine winding sections SIII and SIV are interconnected so thatconductors 18- 27 and 24-27 conduct in opposite directions. Thatopposite interconnection is compensated by the opposite magneticcouplings of winding sections SIII and SIV with the reference. Sinewinding section SI and SIII can be arbitrarily defined to have apositive coupling effect and if so, sine winding sections 811 and SIIIare necessarily defined to have a negative coupling effect.

In a manner analogous to the sine winding sections, the cosine windingsections have positive and negative coupling effects with respect to thereference. Cosine windings CI and CIV may be arbitrarily defined to havea positive coupling effect relative to the reference since current inactive conductor 6-27 is necessarily in the same direction as current inactive conductor 21-27. When winding sections Cl and CIV are defined ashaving a positive coupling effect with respect to the reference, windingsections CII and CIII necessarily have a negative coupling effect.

The cofunction windings 48 of FIG. 1 are an efficient design becauseboth the sine winding sections and the cosine winding sections aresymmetrically disposed on either side of the center line C. Each has anequal number (2) of positive and negative coupling winding sections, onepositive and one negative, on each side of the center line C.Additionally, the number of crossovers for connecting the windingsections in the opposite sense, such as the crossover between terminal77 and 79 (crossing over the connection from active conductor 7-28running to terminal 78), are equal to four. The four crossoverconnections are from terminal 79 to terminal 77, from terminal 82 toterminal 85, from terminal 83 to 84, and from terminal 60' to 60. Thefour crossovers may be reduced to one if the terminal 60 is moved to60', the terminal 64 is moved to 64 and the terminal 63 to 63. Thecrossover may be eliminated by making the terminals 60', 63' and 64' aconnection through to the back (not shown) of member 49, thereby leavingonly the crossover 79 to 77.

In FIG. 4, a cross sectional front view of the schematically shownposition-measuring transformer of FIG. 1 has tripleprimed numbersidentifying analogous parts bearing unprimed numbers in FIG. 1. The sinewinding section SI and cosine winding section CI are shown adjacent theend-detecting winding 30". The height, Hc, of the various activeconductors appropriately postscripted with a -27" and a 28"' in atypical embodiment is appropriately 0.8 inch. The center-tocenterspacing between conductors 1-28' and 1-27' is approximately 0.0l9 inchwhile the center-to-center spacing, E, of the end-detecting windingactive conductors 3-28' and 30-27' is approximately 0.04 inch.

By way of comparison, the height, I-lr, of the active conductors 43" and44 on the reference member 50" is approximately 0.7 inch. Similarly, thecenter-to-center spacing, D, between active conductors 43" and 44" isapproximately 0.02 inch. Note that while the spacing of theend-detecting winding 30' is just twice that of the spacing, D, betweenreference active conductors, the spacing, G, between cofunction activeconductors includes the compression factor useful for reducing theefiects of harmonic signals as described for example in the US. Pat. No.2,799,835.

FIG. 3 depicts a disc drive system employing a positionmeasuringtransformer like that of FIG. 1. The double-primed numbers of FIG. 3correspond to unprimed like-numbers of FIG. 1. The disc drive system ofFIG. 3 includes a translator 89 which supports the transformer member50" which in turn carries the reference winding 51". Translator 89 istranslated by drive 91, typically a motor, thereby translating themember 50" and reference winding 51" relative to the stationary member49" while simultaneously translating the read/write head 92 relative toa magnetic disc 93. Disc 93 is rotated about its center 0 by a drivemeans (not shown). Member 49" is stationary with respect to disc 93 andmotor 91. Member 49" supports the end-detecting windings and cofunctionwindings as previously described in connection with FIG. 1.

The reference winding 51" on member 50", in a typical embodiment, isenergized by a signal generator 87 which may be any suitable andconventional AC signal generator. Signal generator 87 is connected toreference winding 51" via terminals 40" and 41". Signal generator 87 maybe controlled with a start/stop signal via line 72. Line 72 is derivedfrom a control unit 95 described hereinafter.

Member 49" in FIG. 3 includes the end-detecting windings and thecofunction windings 48 described with reference to FIG. 1 but which arenot specifically shown in FIG. 3. The windings on member 49"magnetically couple the relatively movable reference winding 51" onmember 50". Terminals 35" and 36" connect the end-detecting winding 30shown in FIG. 1 to a signal detector 98 in FIG. 3. Similarly, terminals37" and 38", connect the end-detecting winding 31 (shown in FIG. 1) to asignal generator 97 in FIG. 3. Signal detectors 97 and 98 are anyconventional threshold detecting circuits which detect the presence orthe absence of signals in the enddetecting windings. Signal detectors 97and 98 render indications to control 95 via lines 73 and 74,respectively. Signal detectors 97 and 98 typically include bistableflip-flops so that the signals on lines 73 and 74 are appropriatelybi-level signals which indicate the presence or the absence of a signalin the end-detecting windings.

The cofunction windings 48 of FIG. 1 as positioned over the member 49'in FIG. 3 are connected to a sine/cosine detector 99 via terminals 60"and 61" and 63" and 64". Sine/cosine detector 99 typically includesanalog circuitry, such as amplifiers, which sense the level of thesignals from cofunction windings on member 49". Detector 99 conveysthose signals to control 95 via lines schematically represented by asingle line 75.

Control unit 95 is any conventional disc drive control unit which iscapable of carrying out the various control functions necessary for theoperation of the FIG. 3 apparatus. Control 95 typically includes dataprocessing apparatus well known to those skilled in the art of magneticdisc drive systems.

A typical implementation of conventional control 95 includes a digitalcommand source, such as a data processing system, for commandingtranslator 89 to any one of a plurality of discrete track positions forhead 92 between center and the periphery of disc 93. The discrete trackpositions are defined by the positions at which the signals in one orthe other of cofunction windings 48 are a null (or other convenientlevel) relative to the energized reference winding 51".

The command in control 95 is typically stored in a digital register.Another digital register typically represents the present position ofthe reference member 50 and the translator 89. The difference betweenthe command position and the present position is typically stored in athird register which stores, therefore, a how-far-to-go (delta) count.If the delta count differs from 0, a drive signal is commanded via line68, through appropriate amplifier and power-driving circuits (notshown), to cause drive 91 to translate translator 89, reference winding51" and magnetic head 92. Sine/cosine detector 99 detects each cycle (orfraction thereof) of reference winding 51" which translates with respectto member 49". Each detection by detector 99 decrements thehow-far-to-go count in control 95. When the how-far-to-go counterreaches 0 count, the sine or cosine signals (or both) from detector 99are typically employed to directly servo translator 89 to the exacttrack position which was commanded. For a new command, the how-far-to-gocount and decrementing process described is repeated.

Whenever translator 89 receives a signal from line 73 or line 74, thelimit of travel of translator 89 and therefore of head 92 is reached andappropriate control action is taken by control 95. For example, thesignals on line 73 and 74 can invert the polarity of the signal on line68 thereby causing translator 89 to rev erse direction.

Since the subject matter of the control 95 and of the signal detectors97, 98, and 99 are well-known to those skilled in the magnetic disc art,further specific detail is not warranted in this specification. Forfurther details relating to control mechanisms which employ command,present position, and how-far-to-go counters, reference is made toapplication, Ser. No. 814,670 filed Apr. 9, 1969, entitled PositionControl System," and assigned to the same assignee of the presentinvention.

FURTHER AND OTHER EMBODIMENTS While the end-detecting windings 30 and 31of FIG. 1 have been depicted having active conductors which are parallelto the active conductors of the reference winding 51", those activeconductors may be inclined at any angle. Independent of whether theend-detecting windings are parallel or inclined with respect to theactive conductors of the reference windings, the end-detecting windingsare unresponsive to the reference winding except when juxtaposed to theends of the reference winding.

While the present invention has been described with respect to lineartransducers, it of course may apply to rotary devices.

Although the end-detecting windings have been depicted as consisting ofonly two active conductors having twice the spacing of the activeconductors of the reference winding, additional pairs of activeconductors at twice the spacing of the reference winding activeconductors may be interconnected to form an end-detecting winding.Similarly, any integral multiple of twice the spacing (e.g., four, six,eight) may be employed. Any double spacing or multiple thereof isdefined for the purpose of this specification as full-cycle spacing.

While the windings and winding sections of FIG. 1 are generallymanufactured on a single layer, multiple layers may be employed. Forexample, half the cofunction winding sections (e.g., sine) of FIG. 1 maybe manufactured on one layer, and the other half (e.g., cosine) alongwith end-detecting windings 30 and 31 may be added on a second layer.

As heretofore explained, the end-detecting windings are normallyunresponsive to the reference winding, that is, the

resultant signals in the end-detecting windings are zero. A zero levelresultant signal may be considered, in accordance with the presentinvention, to be due to a non-inductive relationship between thereference and end-detecting windings.

While as previously described, the end-detecting windings may beinclined at any angle without losing their unresponsiveness to thereference winding, the parallel relationship between the activeconductors in the end-detecting and reference windings is preferredsince that relationship renders the position measuring transformerinsensitive to minor displacements of one member relative to the othermember in a direction parallel to the active conductors. If inclinedend-detecting windings are employed, then the detection of a limitsignal becomes insensitive to minor shifts between the position-measuring transformer members.

What is claimed is:

1. A position-measuring transformer including first and secondrelatively movable members comprising, a first winding, on said firstmember, formed by first active conductors spaced at half-cycle positionsof a reference cycle and interconnected to cause adjacent ones of saidfirst active conductors to conduct in opposite directions, a secondwinding on said second member inductively coupling said first winding,said second winding formed by second active conductors spaced atfull-cycle positions and interconnected to cause adjacent ones of saidsecond active conductors to conduct in opposite directions, said secondwinding producing a non-zero resultant signal only when said secondactive conductors unequally couple said first winding.

2. The transformer of claim 1 wherein said second active conductors aresubstantially parallel to said first active conductors.

3. The position-measuring transformer of claim 1 further including,

a signal generator for energizing said first winding, and,

a signal detector for detecting any signal induced in said secondwinding.

4. The position-measuring transformer of claim 1 wherein said secondmember further includes,

a first polyphase winding spaced from said second winding for detectingcyclic positions relative to said reference cycle.

5. The position-measuring transformer of claim 4 further including asecond polyphase winding spaced relative to said first polyphase windingany odd integral multiple of onequarter of said reference cycle andwherein each of said polyphase windings includes two winding sectionshaving a positive coupling efi'ect to said reference winding and twowinding sections having a negative coupling effect to said referencewinding.

6. The positiommeasuring transformer of claim 5 wherein each of saidfirst and second polyphase windings has one posi tive coupling and onenegative coupling winding section symmetrically disposed on either sideof a center line whereby the number of conductor crossoversinterconnecting the winding sections does not exceed four.

7. The position-measuring transformer of claim 6 wherein said polyphasewindings include terminals through-connected to the back of said secondmember whereby the number of conductor crossovers equals one.

8. A disc drive system for positioning a magnetic head at a plurality oftrack locations including an inner limit and an outer limit, on amagnetic disc, comprising,

a first member rigidly-fixed with respect to said magnetic head andrelatively movable with respect to said magnetic disc, said first memberhaving a reference winding formed by first active conductors spaced athalf-cycle positions of a reference cycle and interconnected to causeadjacent ones of said first active conductors to conduct in oppositedirections.

a second member rigidly fixed with respect to said magnetic disc havingfirst and second end-detecting windings each having second activeconductors spaced at full-cycle posithird and fourth detectors fordetecting the signals in said member further includes,

first and second polyphase windings each spaced relative to each otherby any odd integral multiple of one-quarter of 10 said reference cycleand wherein each of said polyphase windings includes two windingsections having a positive coupling effect to said reference winding andtwo winding sections having a negative coupling effect to said referencewinding, the said polyphase winding sections formed from activeconductors having a nominal spacing equal to one-half said referencecycle where said track locations are defined by the null positions ofsaid polyphase windings with respect to said reference winding.

10. The disc drive system of claim 9 further including,

a signal generator for energizing said reference windings,

first and second signal detectors for detecting any signals induced insaid first and second end-detecting windings,

. respectively,

first and second polyphase windings, respectively. 1 l.Position-measuring transformer comprising relatively movable inductivelyrelated members in close space relation, one of said members having asingle-phase winding, another of said members having a polyphase windingand a limit winding with first and second active conductors at one endof said polyphase winding, said limit winding being in close space,non-inductive relation with said single phase winding when said singlephase winding is juxtaposed to both said active conductors of said limitwinding, said limit winding being inductively related to said singlephase winding and supplying a limit signal when said single phasewinding is juxtaposed to only one of said active conductors.

l2. Position-measuring transformer comprising relatively movableinductively related members in close space relation, one of said membershaving a single-phase winding formed by reference active conductorsspaced at half-cycle position of a reference cycle, another of saidmembers having a limit winding with first and second active conductorsspaced at full-cycle positions of said reference cycle, said limitwinding being in close-space, non-inductive relation with said singlephase winding when said single-phase winding is juxtaposed to equallycouple both said active conductors of said limit winding, said limitwinding being inductively related to said single phase winding andsupplying a limit signal when said single phase winding is juxtaposed tounequally couple said singlephase winding.

1. A position-measuring transformer including first and secondrelatively movable members comprising, a first winding, on said firstmember, formed by first active conductors spaced at halfcycle positionsof a reference cycle and interconnected to cause adjacent ones of saidfirst active conductors to conduct in opposite directions, a secondwinding on said second member inductively coupling said first winding,said second winding formed by second active conductors spaced atfull-cycle positions and interconnected to cause adjacent ones of saidsecond active conductors to conduct in opposite directions, said secondwinding producing a non-zero resultant signal only when said secondactive conductors unequally couple said first winding.
 2. Thetransformer of claim 1 wherein said second active conductors aresubstantially parallel to said first active conductors.
 3. Theposition-measuring transformer of claim 1 further including, a signalgenerator for energizing said first winding, and, a signal detector fordetecting any signal induced in said second winding.
 4. Theposition-measuring transformer of claim 1 wherein said second memberfurther includes, a first polyphase winding spaced from said secondwinding for detecting cyclic positions relative to said reference cycle.5. The position-measuring transformer of claim 4 further including asecond polyphase winding spaced relative to said first polyphase windingany odd integral multiple of one-quarter of said reference cycle andwherein each of said polyphase windings includes two winding sectionshaving a positive coupling effect to said reference winding and twowinding sections having a negative coupling effect to said referencewinding.
 6. The position-measuring transformer of claim 5 wherein eachof said first and second polyphase windings has one positive couplingand one negative coupling winding section symmetrically disposed oneither side of a center line whereby the number of conductor crossoversinterconnecting the winding sections does not exceed four.
 7. Theposition-measuring transformer of claim 6 wherein said polyphasewindings include terminals through-connected to the back of said secondmember whereby the number of conductor crossovers equals one.
 8. A discdrive system for positioning a magnetic head at a Plurality of tracklocations including an inner limit and an outer limit, on a magneticdisc, comprising, a first member rigidly-fixed with respect to saidmagnetic head and relatively movable with respect to said magnetic disc,said first member having a reference winding formed by first activeconductors spaced at half-cycle positions of a reference cycle andinterconnected to cause adjacent ones of said first active conductors toconduct in opposite directions. a second member rigidly fixed withrespect to said magnetic disc having first and second end-detectingwindings each having second active conductors spaced at full-cyclepositions and interconnected to cause adjacent ones of said secondactive conductors to conduct in opposite directions, said first andsecond end-detecting windings operative to detect ends of said referencewinding to thereby define said inner and outer limits on said magneticdisc.
 9. The disc drive system of claim 8 wherein said second memberfurther includes, first and second polyphase windings each spacedrelative to each other by any odd integral multiple of one-quarter ofsaid reference cycle and wherein each of said polyphase windingsincludes two winding sections having a positive coupling effect to saidreference winding and two winding sections having a negative couplingeffect to said reference winding, the said polyphase winding sectionsformed from active conductors having a nominal spacing equal to one-halfsaid reference cycle where said track locations are defined by the nullpositions of said polyphase windings with respect to said referencewinding.
 10. The disc drive system of claim 9 further including, asignal generator for energizing said reference windings, first andsecond signal detectors for detecting any signals induced in said firstand second end-detecting windings, respectively, third and fourthdetectors for detecting the signals in said first and second polyphasewindings, respectively.
 11. Position-measuring transformer comprisingrelatively movable inductively related members in close space relation,one of said members having a single-phase winding, another of saidmembers having a polyphase winding and a limit winding with first andsecond active conductors at one end of said polyphase winding, saidlimit winding being in close space, non-inductive relation with saidsingle phase winding when said single phase winding is juxtaposed toboth said active conductors of said limit winding, said limit windingbeing inductively related to said single phase winding and supplying alimit signal when said single phase winding is juxtaposed to only one ofsaid active conductors.
 12. Position-measuring transformer comprisingrelatively movable inductively related members in close space relation,one of said members having a single-phase winding formed by referenceactive conductors spaced at half-cycle position of a reference cycle,another of said members having a limit winding with first and secondactive conductors spaced at full-cycle positions of said referencecycle, said limit winding being in close-space, non-inductive relationwith said single phase winding when said single-phase winding isjuxtaposed to equally couple both said active conductors of said limitwinding, said limit winding being inductively related to said singlephase winding and supplying a limit signal when said single phasewinding is juxtaposed to unequally couple said single-phase winding.